Extract common code for computing byte count for images

[David Kilzer (:ddkilzer)]

There are many places where we multiply IntSize.width() * IntSize.height() * 4, so we should pull this into a utility method.

I chose Color.h mostly because it's where "typedef unsigned RGBA32" lives.

[David Kilzer (:ddkilzer)]

Created attachment 292116 [details]
Patch v1

[Simon Fraser (smfr)]

Comment on attachment 292116 [details]
Patch v1

View in context: https://bugs.webkit.org/attachment.cgi?id=292116&action=review

> Source/WebCore/platform/graphics/Color.h:402
> +inline unsigned numBytesWithColor(const IntSize& size)
> +{
> +    Checked<unsigned> result = Checked<unsigned>(size.area()) * sizeof(RGBA32);
> +    return result.unsafeGet();
> +}

I don't think this is a good place, and encourages people to assume sizeof(pixel) == 4 but that might change.

I think each image or buffer object should have a bytesSize() accessor.

[David Kilzer (:ddkilzer)]

Broke out PDFDocumentImage.cpp changes into:

Bug 163757: Use IntSize::unclampedArea() in PDFDocumentImage::updateCachedImageIfNeeded()

[David Kilzer (:ddkilzer)]

Broke out use of checked arithmetic in IntSize::area() as:

Bug 163762: IntSize::area() should used checked arithmetic

[David Kilzer (:ddkilzer)]

Moving to RESOLVED/WONTFIX since there probably needs to be more discussion here before a change is made, and I'm not an area expert.